Selective persistent reduction in choline acetyltransferase activity in basal forebrain of the rat after thyroid deficiency during early life

The effect of thyroid deficiency on the activity of choline acetyltransferase (ChAT; the marker for cholinergic neurons) was studied in different parts of the rat brain at ages 5, 10, 15 and 25 days, and at day 130 following 102 days of rehabilitation. During normal development, the activity of ChAT increased in the cerebral cortex, hippocampus and basal forebrain, and decreased in the cerebellum. Neonatal thyroid deficiency resulted in a marked retardation of the developmental patterns of the enzyme activity. In the hippocampus the effect diminished with age even during the period of thyroid hormone deprivation, while in the cerebral cortex and cerebellum the enzyme activity was restored to normal only after rehabilitation. In contrast, ChAT activity in the basal forebrain remained persistently reduced in comparison with controls. The results indicate that neonatal thyroid deficiency causes selective irreversible biological damage to subcortical cholinergic neurons.     

Nerve growth factor facilitates conditioned taste aversion learning in normal rats

Chronic intracerebroventricular (i.c.v.) infusion of 3.2 μg/day of nerve growth factor (NGF) in normal rats elevated choline acetyltransferase (ChAT) activity of the striatum, medial septum, and basal forebrain and improved performance of a conditioned taste aversion (CTA) task. Relative to bovine serum albumin (BSA) or Cytochrome C treatments, NGF treatment facilitated acquisition and prolonged extinction of a lithium chloride (LiCl)-induced saccharin aversion. This facilitation was evident at saccharin/LiCl intervals ranging up to 1 h. Also, NGF treatment did not increase reactivity to LiCl-induced illness and neither shifted detection thresholds nor altered hedonic reactions to taste stimuli, indicating that NGF did not produce simple changes in sensory function. NGF treatments that elevate ChAT also facilitate memory of CTA in normal, adult rats.     

Choline acetyltransferase immunopositive neurons in the lateral septum

A small cluster of choline acetyltransferase (ChAT)-positive neurons was identified immunohistochemically in rat and monkey brain in the ventral portion of the lateral septal nucleus. These multipolar neurons were smaller and much less intensely staining than the medial septal nucleus ChAT-immunopositive group.     

Cytochemical characteristics of cat spinal neurons activated during fictive locomotion

Using standard immunohistochemical and histochemical techniques, we have examined the neurochemical characteristics of a subpopulation of locomotor-related neurons as labeled by the activity-dependent marker c-fos. Results were compared to those obtained from a small sample of intracellulariy labeled locomotor-related neurons. In the paralyzed, decerebrate cat, fictive locomotion was evoked by electrical stimulation of the mesencephalic locomotor region. Most c-fos-immunoreactive neurons were distributed in medial lamina VI and VII and in lamina VIII and X. Double labeling of c-fos with various cytochemical markers revealed that about one-third of the c-fos-immunoreactive neurons were choline acetyltransferase immtmoroactive, about one-third were glutamate immunoreactive, and about one-third were aspartate immunoreactive. In addition, approximately 15% of the c-fos-labeled neurons contained NADPH-diaphorase reaction product, while almost 40% appeared to receive close contacts from calcitonin generelated peptide-immunoreactive fibers and boutons. Choline acetyfransferase- or aspartate immunoreactivity was observed in some intracellulariy, labeled neurons. These findings have implications regarding the putative neurotransmitters utilized by subpopulations of locomotor-related neurons in the cat spinal cord.     

Collateral axons of cholinergic pontine neurones projecting to midline, mediodorsal and parafascicular thalamic nuclei in the rat

The organization of collateral axons projecting from neurones in the pontine laterodorsal tegmental nucleus (LDTg) has been examined using combinations of retrograde neuronal tracers with immunocytochemical markers for the acetylcholine-synthesizing enzyme choline acetyltranferase (CHAT), focussing on projections to the midline, mediodorsal and parafascicular thalamic nuclei and the ventral tegmental area. 25–59% of LDTg neurones projecting to the mediodorsal nucleus provided collaterals to the midline nuclei. Virtually all (87–96%) of these double retrogradely labelled neurones appeared cholinergic. 9–18% of LDTg neurones projecting to the parafascicular nuclei also provided a collateral to the midline nuclei and 50–78% of these double retrogradely labelled neurones stained for CHAT. 26–29% of the single LDTg neurones which projected collaterals to both the mediodorsal and midline nuclei, were found to project a third collateral to the ventral tegmental area. These anatomical findings, taken together with functional evidence, suggest that cholinergic terminals arising from LDTg are involved in coordinating thalamic mechanisms of brain state control; and in regulating dopaminergic pathways, both directly and via the thalamus.     

Ultrastructural localization of acetylcholinesterase and choline acetyltransferase in oligodendrocytes, glioblasts and vascular endothelial cells in the external cuneate nucleus of the gerbil

This study reports the reactivities of acetylcholinesterase (AChE) and choline acetyltransferase (ChAT) in some of the nonneuronal elements in the external cuneate nucleus (ECN) of gerbils. AChE reaction products were localized in some oligodendrocytes in their cisternae of rough endoplasmic reticulum, nuclear envelope and Golgi saccules. The basal lamina lining the capillary endothelia also displayed AChE reactivity. In ChAT immunocytochemistry, the reaction products were found to be associated with the vascular basal lamina as well as the endothelial plasma membrane facing the lumen. The most remarkable finding was the localization of ChAT immunoreactivity in some oligodendrocytes and occasional glioblasts (small glial precursor cells containing a thin rim of cytoplasm surrounding an irregular nucleus with homogeneous chromatin materials). The ChAT-positive oligodendrocytes consisted of two types, medium-dense and dark cells, either associated with blood vessels or ChAT-stained neuronal elements. It is suggested from these new findings that at least some of the oligodendrocytes and glioblasts in the ECN of gerbils may be involved in the synthesis, storage, release and degradation of acetylcholine.     

Nimodipine prevents the in vivo decrease in hippocampal extracellular acetylcholine produced by hypobaric hypoxia

Hypoxia decreases acetylcholine (ACh) synthesis and release in vitro, and ACh synthhesis in vivo; however, its effect on extracellular concentration of ACh in vivo is not known. The calcium channel blocker nimodipine is a cerebrovascular dilator which also increases extracellular ACh in vivo. Therefore, it may provide protection from the effects of hypobaric hypoxia on the cholinergic system either via its effects on vascular function or by direct action on the nervous system. This study examined the effect of hypobaric hypoxia on extracellular ACh and choline levels, as measured by microdialysis, as well as the effects of nimodipine under hypoxia. Microdialysis guide cannulae were implanted into the hippocampal region of male Fischer rats so that probes would sample from the CA1 and DG regions. Animals were then exposed for eight hours to a simulated altitude of 5,500 m (18,000 ft) or tested at sea level for an equivalent duration. HPLC with electrochemical detection was used for analysis of the dialysates. At 5,500 m extracellular ACh levels in the placebo-treated group were significantly lower than the sea level group values. This decrement was reversed by nimodipine administered i.p. immediately preceding altitude ascent (10 mg/kg) and 250 min post-altitude ascent (10 mg/kg). These data suggest that nimodipine may provide protection from the detrimental effects of hypoxia on hippocampal cholinergic function.     

A comparison of the distribution of central cholinergic neurons as demonstrated by acetylcholinesterase pharmacohistochemistry and choline acetyltransferase immunohistochemistry

The topographical distribution of cholinergic cell bodies has been studied in the rat brain and spinal cord by choline acetyltransferase (ChAT)-immunohistochemistry and acetylcholinesterase (AChE)-pharmacohistochemistry using diisopropylfluorophosphate (DFP). The ChAT-containing cells and the cells that stained intensely for AChE 4-8 hr after DFP were mapped in detail on an atlas of the forebrain (telencephalon, diencephalon) hindbrain (mesencephalon, rhombencephalon) and cervical cord (C2, C6). Striking similarities were observed between ChAT-positive cells and neuronal soma that stained intensely for AChE both in terms of cytoarchitectural characteristics, and with respect to the distribution of the labelled cells in many areas of the central nervous system (CNS). In the forebrain these areas include the caudatoputamen, nucleus accumbens, medial septum, nucleus of the diagonal band, magnocellular preoptic nucleus and nucleus basalis magnocellularis. In contrast, a marked discrepancy was observed in the hypothalamus and ventral thalamus where there were many neurons that stained intensely for AChE, but where there was an absence of ChAT-positive cells. No cholinergic perikarya were detected in the cerebral cortex, hippocampus, amygdala and dorsal diencephalon by either histochemical procedure. In the hindbrain, all the motoneurons constituting the well-established cranial nerve nuclei (III-VII, IX-XII) contained ChAT and exhibited intense staining for AChE. Further, a close correspondence was observed in the distribution of labeled neurons obtained by the two histochemical procedures in the midbrain and pontine tegmentum, including the laterodorsal tegmental nucleus, some areas in the caudal pontine and bulbar reticular formation, and the central gray of the closed medulla oblongata. On the other hand, AChE-intense cells were found in the nucleus raphe magnus, ventral part of gigantocellular reticular nucleus, and flocculus of the cerebellum, where ChAT-positive cells were rarely observed. According to both techniques, no positive cells were seen in the cerebellar nuclei, the pontine nuclei, or the nucleus reticularis tegmenti pontis. Large ventral horn motoneurons and, occasionally, cells in the intermediomedial zone of the cervical cord displayed ChAT-immunoreactivity and intense AChE staining. On the other hand, AChE-intense cells were detected in the dorsal portion of the lateral funiculus, but immunoreactive cells were not found in any portion of the spinal cord white matter.(ABSTRACT TRUNCATED AT 400 WORDS)     

Six-hydroxydopamine induced hyperactivity: neither sex differences nor caffeine stimulation are found

We investigated possible sex differences in the development of locomotor activity in rats treated neonatally with desmethylimipramine (DMI) followed by intraventricular 6-hydroxydopamine (6-HDA). In addition, the locomotor response to the stimulant caffeine was investigated in the male rats after they had reached adulthood. Both male and female 6-HDA-treated rats exhibited increased activity relative to controls. No sex differences were seen in either the development or magnitude of this effect. Male rats were used to determine the dose effects function for caffeine (0.5, 5, 15, 30 mg/kg) on locomotor activity. Control rats exhibited increased locomotor activity whereas 6-HDA-treated rats showed no increases with any dose of caffeine. Large decreases in the dopamine content of the olfactory tubercle (-88%, -82%), nucleus accumbens (-96%, -95%), and striatum (-99%, -99%) were found in both male and female rats. Choline acetyltransferase and glutamic acid decarboxylase activities were unchanged.     

Expression of estrogen receptor-like immunoreactivity by different subgroups of basal forebrain cholinergic neurons in gonadectomized male and female rats

Recent studies have demonstrated that estrogen administration can produce significant increases in relative levels of choline acetyltransferase (ChAT) mRNA and protein in specific regions of the female, but not the male, rat basal forebrain. In the present study immunocytochemical techniques were used to identify and compare relative numbers of cholinergic neurons containing estrogen receptors within the medial septum, horizontal limb of the diagonal band of Broca, nucleus basalis magnocellularis, and striatum of gonadectomized male and female rats to determine whether there are differences in the percentage of cholinergic neurons expressing estrogen receptors which might contribute to the different regional- and sex-specific effects of estrogen which have been described. Counts of choline acetyltransferase-immunoreactive cells revealed significant regional differences in the average number of cholinergic neurons/section; however, no difference between males and females in the numbers of cholinergic neurons in each of the four regions analyzed was observed. Fifty to eighty percent of the cholinergic neurons detected in both males and females contained estrogen receptor-like immunoreactivity. A small but significant difference between males and females was detected with females having slightly more (10.5%) double-labeled cells than males overall. Individual comparisons revealed that significantly more (18–33%) double-labeled cells were detected in the horizontal limb of the diagonal band, but not in the medial septum, nucleus basalis, or striatum of females vs. males. There was also a small but significant regional difference in the percentage of double-labeled cells with the highest percentage (74.2%) detected in the striatum and the lowest percentage (63.4%) detected in the horizontal limb. None of these differences appear to account for the regional- and sex-specific effects of estrogen on cholinergic neurons which have been observed. We conclude that differences in the effects of estrogen on cholinergic neurons in males vs. females and in different Subregions of the female basal forebrain are not due to differences in the percentage of cholinergic neurons expressing estrogen receptors.